1) Field of the Invention
The present invention relates to a technology for keeping image quality precision of both sides of a recording medium in an image forming apparatus.
2) Description of the Related Art
An ordinary image forming apparatus equipped with a double-side printing function performs double-side printing by transferring an image of a first page, formed on a photoconductor, onto a sheet of paper, fixing the image, then temporarily retaining the sheet in a double-side inverting sheet feeder, feeding the sheet from the double-side inverting sheet feeder in synchronism with the timing of an image of a second page formed again on the photoconductor, transferring the image of the second page onto the sheet, and fixing that image.
Double-side printing onto a sheet of paper using the scheme inevitably requires a double-side inverting sheet feeder and suffers slow first printing in double-side printing since after printing on one side is performed and the sheet is turned over, printing is performed on the other side.
There is an image forming apparatus which has an image forming unit, a transfer unit, and a fixing unit for each side of a sheet on which double-side printing is performed so as to be able to perform double-side printing without using a double-side inverting sheet feeder as a countermeasure to this problem (see, for example, Japanese Patent Application Laid-Open No. 2000-352889).
As the apparatus in the Japanese Patent Application Laid-Open No. 2000-352889 has an image forming unit, a transfer unit, and a fixing unit exclusively for printing on each side of a sheet, however, the mechanical size inevitably becomes large and the cost increases accordingly.
A difference in image quality may occur originated from the number of image transfers and time-variant characteristics of the individual image forming units, transfer units, and fixing units.
Since the configuration for performing double-side printing without using a double-side inverting sheet feeder to speed up double-side printing uses different image forming paths for the respective sides of the sheet, a difference in image quality may occur between the two sides due to the number of image transfers and time-variant characteristics.